Non-invasive Providencia alcalifaciens strains fail to attach to HEp-2 cells

We investigated the adherence properties of six P. alcalifaciens strains wi th previously characterized differential invasive capabilities in HEp-2 cel ls. Highly invasive strains were found to attach to HEp-2 cell monolayers w ithin 2 h post-infection and in large numbers on the eukaryotic cell surfac es within 3 h post-infection. In contrast, weakly or non-invasive P. alcali faciens strains were non-adherent to HEp-2 cells even at 3 h post-infection . Highly invasive isolates were found to weakly bind F-actin using the fluo rescent actin staining assay although these strains were negative for Esche richia coli attachment and effacing gene (eaeA) of enteropathogenic E. coli (EPEC). These results suggest that the strain variation in the ability of P. alcalifaciens to invade HEp-2 cells previously noted by several investig ators may be linked to expression of key adhesin(s) on the cell surface of invasive isolates.